As a general rule of thumb, the least you can do is to limit yourself to one or fewer biological offspring. By all means, adopt the hell out of more! Seriously, if you really want to reduce your "carbon footprint" and every other measurement of pollution and waste, you have to stop breeding. Otherwise, you're increasing the problems of the world exponentially. If we don't do this voluntarily, Nature will do this anyway, and Nature will do it in ways we won't find pleasant (i.e. starvation, natural disaster, polar ice caps melting us into an ice age, not enough water to go around, suffocation on dirty air, etc.) In fact, many people around the world are already finding this out first hand, mostly due to our (American's) over consumption. All of our over consumption literally already makes us murderers through our ignorance, greed, and disregard.
Anyway, you should strongly consider having no children at all if you are not an extremely valuable member of the human race, and I find that a surprisingly high, though certainly not nearly high enough, number of you know who you are. I mean anyone in the 90th percentile, an IQ below about 125, please, please, consider condoms. The government should really pay for sterilization and birth control for these people, but we all need to start doing our part in the meantime.
Of course the best thing you can do is to kill yourself, or if that's a bit too harsh for you, at least sign a DNR and refuse medical treatment for degenerative diseases such as cancer and diabetes. You'll be much happier for your remaining years if you can eat your Cocoa Puffs, I'm sure.
It turns out the "bad guys", the gang in the silly Mormon film from the late 1970s, Saturday's Warrior, were right on when they sang "Zero population is the answer my friends - without it the rest of us are doomed!" Except of course, at this point, zero population isn't going far enough.
Here are some videos on the topic:
First, a charming, simple explanation of some of the problems involved:
Only the first few minutes of this one are about overpopulation, though the whole of it is interesting:
